The chairman of US private security contractor Blackwater has defended his firm and his staff during a grilling by a congressional committee.

Blackwater has come under scrutiny since a shoot-out last month in Baghdad in which 11 Iraqis were killed. The FBI has begun investigating that incident.

The firm's founder, Erik Prince, said his staff were brave and effective, and had acted "appropriately".

But one of the committee asked if the firm was "a shadow mercenary force".

"Blackwater appears to have fostered a culture of shoot first - and sometimes kill - and then ask the questions," said Democratic Congressman Elijah Cummings.

Blackwater is the main firm employed by the state department to provide security for its staff and visiting officials and businessmen.

It has earned more than $1bn (£490m) from US government contracts since 2001. The state department paid the company more than $832m (£408m) for security work between 2004 and 2006.

'Short' on standards

The 16 September shooting incident is not featuring in the hearing by the Committee on Oversight and Government Reform, following a Justice Department request that it wait until the FBI's investigation is concluded.

CONGRESS BLACKWATER REPORT

Earned more than $1bn (£490m) from US government contracts since 2001

Staff involved in 195 shootings in Iraq between 2005 and 12 September 2007

Allegedly drunk employee killed Iraqi vice-president's guard in 2006, but was flown out of Iraq and faced no criminal charges

Several representatives referred to an incident in which a Blackwater guard shot dead a bodyguard of one of Iraq's vice-presidents while drunk. He was hurried out of Iraq and faced no criminal charges.

They said the incident showed how "unaccountable" Blackwater and other firms were.

"Why are we privatising our military to an organisation that has been aggressive and in some cases reckless in the handling of their duties?" asked New York Democrat Carolyn Maloney.

BLACKWATER USA FACTS

Founded in 1997 by a former US Navy Seal

Headquarters in North Carolina

One of at least 28 private security companies in Iraq

Employs 744 US citizens, 231 third-country nationals, and 12 Iraqis to protect US state department in Iraq